import pandas as pd
df=pd.DataFrame({'商品':['苹果','香蕉','梨'],
                 '单价(元)':['5','5','4'],
                 '销量(kg)':['100','None','None'],
                 '库存(kg)':['50','None','70']})
print('原始数据: \n', df)
print('检查缺失值: \n', df.isnull())
print('检查非缺失值: \n', df.notnull())
print('统计每列缺失值的个数: \n', df.isnull().sum())